Unfortunately the data is in rows rather than columns, so the filter
is not easily applied.

The cells are, to quote the finance guy, "highlighted", looking at the
cells he appears to have filled using Format Cells. They all have
values and only get shaded once the bill has been sent out. What I was
hoping for was somthing like
=SUMIFS(A3:A15,CellColour="Blue") in the Billed to date column
and
=A2-(SUMIFS(A3:A15,CellColour="Blue") in the Remaining column,
where A2 contains the total amount to be billed.

Fred